This invention relates to methods and apparatus for optically inspecting products, and more particularly to methods and apparatus for determining whether or not a product has predetermined optically detectable characteristics.
Certain high-volume, mass-produced consumer products are made in such large quantities and at such high speeds that conventional inspection methods are either impractical or impossible. Nevertheless, it is important to ensure that the products are satisfactory in appearance, quality, etc. For example, cigarette packages may come off a cigarette-making machine at the rate of 360 per minute, and cigarette manufacturers are attempting to achieve substantially greater speeds (e.g., 750 packages per minute or more). At these speeds, it is extremely difficult, using conventional inspection techniques, to make sure that the packaging for each pack has been properly folded around the cigarettes, that the printing on the packaging is properly aligned and centered, that the tax stamp has been applied and is properly centered and aligned, that the tear strip is present and properly located, etc. Similar inspection problems occur in the production of many other products such as packaged foods and beverages, toilet articles and medicines, soaps and detergents, paper products, magazines, books, etc.
Illustrative of the shortcomings of conventional inspection methods and apparatus are the difficulties encountered in attempting to use the conventional electro-optical technique of having multiple photocells monitor the optical properties of the product at a multiplicity of points on the surface of the product. Among the difficulties with this technique at high product speeds is the fact that it may be extremely costly or even impossible to process the resulting data sufficiently rapidly to keep up with the product stream. Another problem with this technique is that it is typically very sensitive to slight variations in product location or orientation on the apparatus which is conveying the product through the inspection station. In other words, the product may be erroneously identified as not having the predetermined optical characteristics simply because of variability in the conveyor apparatus. Conventional systems employing a camera or similar two-dimensional detector array sensor to provide an image of the object have similar deficiencies.
In view of the foregoing, it is an object of this invention to provide improved product inspection methods and apparatus.
It is a more particular object of this invention to improve the speed, performance, and flexibility of product inspection methods and apparatus by performing more of the necessary information processing optically.